**1. Introduction**

368 Biogas

Samer, M. (2010). A Software Program for Planning and Designing Biogas Plants. *Transactions of the ASABE*, Vol. 53, No. 4, pp. 1277-1285, ISSN 2151-0032 Samer, M. (2008). *An Expert System for Planning and Designing Dairy Farms in Hot Climates*,

Samer, M.; Grimm, H.; Hatem, M.; Doluschitz, R. & Jungbluth T. (2008). Mathematical

Modeling and Spark Mapping for Construction of Aerobic Treatment Systems and their Manure Handling System, *Proceedings of International Conference on Agricultural Engineering*, Book of Abstracts p. 28, EurAgEng, Hersonissos, Crete,

Dissertation, VDI-MEG, ISSN 0931-6264, Script 472

Greece, June 23-25, 2008

In the following sections, recommendations supported by schematics are given for the injection of compliant processed biogas into natural gas grids. Based on the characteristics of the natural gases distributed in Germany and taking into account the applicable


In order to feed biogas into a natural gas grid, unwanted components need to be removed from the gas and the burning properties of the gas need to be adjusted to those of the rest of the gas in the grid. In this way, the correct operation of the gas-burning appliances and the accuracy of the billing of retail customers is assured.

The purified biogas is conditioned depending upon the properties of the base gas (Fig.1). In the case of L gas, the calorific value or Wobbe index is realised by adding air, or air and LPG. In the case of H gas characteristics, the addition of LPG is required to adjust the calorific value to that of the usually higher calorific H base gas.

Fig. 1. gas conditioning by air and LPG addition

Conditioning of Biogas for Injection into the Natural Gas Grid 371

When considering equation 2 and table 1, it is clear that even small volumes of higher hydrocarbons affect the parameters of combustion of the gas mixture, due to the greater

CH4 (Methane) 0,7175 11,064 C2H6 (Ethane) 1,3551 19,537 C3H8 (Propane) 2,010 28,095 C4H10 (Butane) 2,709 37,252 CO2 1,9767 0 Air 1,293 0

In addition to the basic requirements for the gas properties, limits for accompanying

Hydrocarbons: Condensation point °C Soil temperature at the respective Water: dew point °C Line pressure Fog, dust, liquid Technically free

> % %

**Gas Accompanying Substances Indicative maximum** 

(excluding odorants) mg/m3 <sup>30</sup> Mercaptan mg/m3 6 short-term mg/m3 16 Hydrogen sulphide mg/m3 5 In exceptional cases, briefly mg/m3 10 Table 2. Permitted substances in the gas according to DVGW worksheet G 260 (DVGW,

Important boundary conditions are determined by the dew points, the oxygen content and the sulphur content. Information on the dew points is formulated so that condensation can be excluded. As far as the oxygen content is concerned, the grids in Germany can be regarded as dry and therefore the limit of 3 vol -% is to be applied. It should be noted at this point that at the long-range transport level significantly lower O2contents, usually in the low ppm range are to be observed (EASEE gas, CPB European Association for the Streamlining of Energy Exchange-gas Common Business Practice, 2005) for cross-border distribution (H

The raw gas must be cleaned, processed (according to G 260) and compressed to the pressure of the grid operator. Under no circumstances should health risks arise from processed gas. For injection into the distribution network of a local GU, the gas must be

ρ**n in kg/m3 HS,n in kWh/m3**

3 0,5

density and calorific values. The same applies to air and carbon dioxide.

Table 1. Standard density and calorific value of the main components

Percentage of oxygen in dry distribution networks - In humid distribution networks

> Total sulphur Annual mean value

2008)

gas).

substances are specified in worksheet G 260, which may not be exceeded.

Schematic recommendations include the answers to the key questions listed below and allow a simple "read out" of the target properties, taking into account the current regulatory requirements. Gas utilities (GU) and operators can already in the planning phase determine the feed options and requirements with the help of the graphs. The key questions are:


The following conditions are to be observed in addition to point 1 : Engine applications, natural gas filling stations (methane, K number, condensation of higher hydrocarbons) and industrial customers.
